Deep-Investigated Analytical Modeling of a Surface Permanent Magnet Vernier Motor

Permanent magnet Vernier motors (PMVMs) possess the advantage of high torque density for high-performance applications. However, the low power factor challenge makes it unacceptable for direct-drive applications. A lack of accurate modeling method based on the motor sizing law, i.e., air-gap flux density, linear current density, and motor geometry parameters, raises difficulties for machine designers to further conduct research on the performance metrics. This article presents a deep investigation into the analytical modeling technique for surface PMVMs (SPMVMs). It can identify an accurate approach to obtain the performance metrics, including electromagnetic torque and power factor. The modeling technique is developed based on the conformal mapping method. By using this, both radial and tangential permeability functions can be calculated to obtain the motor magnetic loading accurately, considering the leakage flux. The slotting effect on both air-gap flux density and armature-winding function is analyzed to achieve a precise formula for torque and power factor computations. The new modeling technique is applied to integral-slot SPMVMs with different slot/pole combinations, gear ratios, slot openings, and magnet thick-ness to evaluate the impacts of motor parameters on high-power-factor and high-torque-density designs. Finally, an SPMVM with the characteristics of high torque density and power factor is fabricated to verify the analytical model at the power rating of 0.8 kW and the speed of 500 r/min. The experimental results show that the prototype exhibits a high power factor of 0.9 and high torque density 22.5 Nm/L.

Automated summary

Permanent magnet Vernier motors (PMVMs) have high torque density advantage for high-performance applications, but the low power factor challenge makes it unsuitable for direct-drive applications. This article presents an accurate modeling technique based on the conformal mapping method to obtain the performance metrics of PMVMs. The technique calculates both radial and tangential permeability functions, considering leakage flux and slotting effect, to achieve precise torque and power factor computations. Experimental results on a fabricated PMVM prototype confirm the high power factor and torque density achieved by the analytical model.